Speed control means for d.c. motors and method for making the same



April 18, 1967 J R. MOORE, JR 3,315,105

SPEED CONTiiOL MEANS FOR D.C. MOTORS AND METHOD FOR MAKING THE SAMEOriginal Filed April l8, 1963 INVENTORI BY JAMES R. MOORE,JR.

ATTVS.

United States Patent 3,315,105 SPEED CONTROL MEANS FOR D.C. MOTORS ANDMETHOD FOR MAKING THE SAME James Riley Moore, Jr., Columbus, Miss.,assignor to American Bosch Arma Corporation, Columbus, Miss.,

a corporation of New York Continuation of application Ser. No. 265,961,Mar. 18, 1963. This application Nov. 9, 1965, Ser. No. 510,393 2 Claims.(Cl. 310-211) This is a continuation application of my prior U.S.application Ser. No. 265,961, filed Mar. 18, 1963, now abandoned forSpeed Control Means for D.C. Motors and Method for Making the Same.

This invention relates to armatures for electric motor apparatus, suchas, direct current, series wound electric motor apparatus. Moreparticularly the present invention relates to new and improved armaturemeans for controlling the speed characteristics of such motor apparatusin a manner to prevent overspeed or runaway conditions when the motor isunder comparatively light load or no load and to a method of making sucharmature means.

0 well-known characteristic of direct current, series wound electricmotors is that they possess a high stall or starting torque as comparedfor example, to shunt or compound wound motors and accordingly they areoften employed for example in window lift and seat mover installationsfor automobiles or the like where the load on the motor may vary from acomparatively heavy starting load to a substantially no-load condition.A drawback of the series wound motor in these applica tions is that ittends to overspeed or runaway when the load on the motor iscomparatively small. When running at excessively high speeds, the seriesmotor tends to be noisy and in some instances there is the possibilityof damage to the armature windings.

Various attempts have been made in the past to solve this problem ofrunaway in direct current, series wound motors, but these proposals havenot been entirely satisfactory] For example one proposed solution to theproblem consists in the use of mechanical means such as a spring orbowed washer engaging the armature shaft to provide a mechanical orfriction load thereon. However, since the load imposed by the washer ispresent regardless of armature speed, it has the disadvantage of loadingthe armature at times when it is not needed and even not wanted, forexample, during initial starting of the motor when high stall orstarting torque is desired. In accordance with other attempts to solvethe problem, it has been proposed to provide short-circuited armaturewindings. However, such armature assemblies of the prior art arecomparatively expensive to manufacture and in some instances, cut downon the overall performance of the motor and/ or cause an unbalancedcondition contributing to undue wear on the motor. In still otherinstances it has been proposed to wedge bars or strips of conductingmaterial forcibly into each of the slots of the armature between theouter tips of the fingers of the rotor assembly and the armaturewindings. This assembly, however, is comparatively expensive tomanufacture.

With the foregoing in mind, it is an object of the present invention toprovide a new and improved armature assembly for electric motorapparatus such as direct current, series wound motors which effectivelyeliminates the danger of runaway or overspeeding and yet preserves thedesired high starting torque characteristic thereby precludingobjectionable noises and damage to the motor under little or no-loadconditions.

A further object of the present invention is to provide an armatureassembly providing speed control means 3,315,105 Patented Apr. 18, 1967preventing runaway which is of comparatively simplified construction sothat it may be assembled easily, manufactured economically and which isextremely effective for the purposes intended.

Another object of the present invention is to provide a new and improvedmethod for fabricating in an economical manner an armature incorporatingspeed control means.

These and other objects of the present invention and the variousfeatures and details of the construction and operation thereof arehereinafter more fully set forth with reference to the accompanyingdrawings, in which:

FIG. 1 is a side elevational view of an armature constructed inaccordance with the present invention;

FIG. 2 is an enlarged end view of the armature with parts broken away toshow details of the construction of the armature more clearly;

FIG. 3 is an enlarged fragmentary view of a portion of the rotor of thearmature;

FIG. 4 is a sectional view taken on line 44 of FIG. 3; and

FIG. 5 is a perspective view of a current conducting liner for insertionin one or more of the armature slots.

Referring now to the drawings, there is shown in FIG. 1 an armature 10for a motor apparatus, such as, a series wound motor which embodiesspeed control means in accordance with the present invention. Thearmature 10 comprises a rotor assembly 12 mounted on a shaft 14. Therotor assembly 12 consists of a laminated core structure comprised of aplurality of thin laminations or plates 16 as shown in FIG. 4, eachhaving a plurality of radially extending, circumferentially spaced,T-shaped fingers 18. The fingers 18 of the laminations of the corestructure are aligned to provide a plurality of axially extendingU-shaped slots 20 to receive the armature windings such as 22.

It has been found that when the armature 10 rotates in a magnetic fieldin a motor assembly, a voltage is induced in the laminations 16 of therotor assembly which results in a current flow within each lamination 16and from lamination to lamination. This induced current fiow produces amagnetic field opposing the normal magnetic field of the armaturewindings 22 which causes the armature to rotate thus tending to slow themotor. The amount of induced current flow in the laminations 16 of therotor assembly is proportional to the speed at which the armature 10rotates and hence the slowing action becomes higher at higher speeds.However, even though the laminations are mounted in close face-to-facerelation, there is a comparatively poor electrical contact between thelaminations due, for example, to small particles therebetween andsurface irregularities in the confronting surfaces of adjacentlaminations. Accordingly, the magnetic field produced by the inducedcurrent flow in the laminations 16 is comparatively weak and does notappreciably affect the normal magnetic field of the armature windings 22and actually does not slow down the motor. Thus under small or no-loadconditions, the motor has a tendency to overspeed" or runaway.

In accordance with the present invention, means is provided fordecreasing the electrical resistivity of the laminations 16 of the rotorassembly 12 in a direction parallel to the slots 20' thereby to increasethe induced current flow in the rotor assembly, thus providing amagnetic field opposing the normal magnetic field of the armaturewindings 22 which not only increases proportionately with increasedarmature speed, but is of a sufficient magnitude at high armature speedsto prevent runaway. Accordingly an elfective speed control of thearmature is provided by the induced magnetic field, the maximum controloccurring at the higher speeds of the armature where the danger ofrunaway or overspeeding exists, while the opposing magnetic field beingminimal at the lower speeds to preserve the high stall or startingtorque characteristics of the motor. In the present instance this isaccomplished by providing a current conducting member in the form of aliner 30 in one or more of the axial slots 20 in contact with thesurface of each of the laminations facing the slot. In the presentinstance, the liner 30 comprises a thin, flexible layer 32 of a materialhaving high electrical conductivity, such as copper, of a suitable sizeand shape to engage substantially the entire edge surface of theadjacent fingers 18 of the laminations 16 forming an axial slot 20, anda sheet 34 of insulating material such as paper of substantially thesame size and shape as the layer 32 disposed between the armaturewindings 22 and the layer 32. In the present instance the sheet 34 ofinsulating material and the layer 32 of conducting material are bondedtogether to form an integral assembly. However, they may be separateelements.

In accordance with the present method of assembling the armature 10, thelaminations 16 are pressed onto the shaft 14 with the fingers 18 alignedto define the axial slots 20. Thereafter the liner 30, composed of thethin layer 32 of copper or the like and sheet of paper 34, which isgenerally rectangular in form is bent so that it is generally U-shapedin cross section and then inserted into at least one of the axial slots20. The outer ends of the liner are then crimped outward to provideturned back end edges 36 overlying the end face of the laminations atouter ends of the core structure as shown. Thereafter, the armaturewindings 22 are wound on to the laminated core in the conventionalmanner. During assembly of the windings 22, the layer 32 of the liner 30is pressed into close engagement with the edges of the laminations 16facing the slot 20, thus decreasing the electrical resistivity of thecore structure and providing for good flow of the current induced in thelaminations, the sheet 34 serving to insulate the armature windings fromthe layer 32 of conducting material.

By this arrangement the layer 32 of conducting material, which is inintimate contact with each of the laminations '16 of the stack, servesto short circuit each lamination 16 to the next adjacent lamination 16thus decreasing the total electrical resistivity of the laminated core.By thus decreasing the electrical resistivity, the resistance to fiow ofthe induced current flow is decreased. Accordingly, as the armaturerotates in a magnetic field, a relatively strong current is induced inthe laminated core which produces a magnetic field opposing the normalmagnetic field of the armature windings, the induced magnetic fieldbeing proportional to the armature speed. At high armature speeds, theeffect of the induced magnetic field opposing the normal magnetic fieldis greatest, thereby to prevent runaway or overspeeding. In theillustrated embodiment, a liner 30 is provided in each of three slots 20of the rotor assembly. If desired, a lesser or greater number of liners30 may be employed depending on the speed control wanted.

The improved induced current flow provided by the liner 30 may also beemployed advantageously in applications where motor apparatus isrequired to provide dynamic braking. The dynamic braking referred to isprovided by the current generated within the motor apparatus in theabsence of externally applied armature winding current, which tends toarrest turning of the armature. In the present instance, the improvedcurrent flow in the laminations tends to increase the rate ofdeceleration of the armature thus providing dynamic braking. In thisregard it is of course to be understood that when used to effect dynamicbraking, the liner may be used in motors other than direct current,series wound motors.

While a particular embodiment of the present invention have beenillustrated and described herein, it is not intended to limit theinvention to such disclosure and changes and modifications may be madetherein within the scope of the following claims.

I claim:

1. A balanced rotor assembly for an armature comprising a core structureincluding a plurality of laminations each having a plurality of spacedapart fingers, said laminations arranged in face-to-face relation withthe fingers aligned to define a plurality of slots extendingtransversely of the laminations, a plurality of circumferentiallyequispaced liners mounted in said slots, said liners being ofsubstantially the same configuration and weight and all of said linersbeing substantially equispaced from the axis of rotation of said rotor,at least one of said liners being a thin laminated liner consisting of athin layer of electrically conductive material having one face incontact with a plurality of said laminations and a thin sheet ofinsulating material confronting and bonded to the face of said layeropposite said one face and an armature winding in said slots pressingsaid one liner into engagement with said laminations thereby to decreasethe electrical resistivity of said core structure, said one liner havingan open side aligned with the slot and being readily deformable underthe pressure of the windings and said windings being tightly woundwhereby the direct con tact between the layer of electrically conductivematerial of said one liner and said laminations constitutes the soleelectrical connection therebetween and said winding being exposedthrough said slots.

2. A balanced armature assembly comprising a shaft, a plurality oflaminations defining a core structure mounted in face-to-face relationon said shaft, each of said laminations having a plurality of radiallyextending, circumferentially spaced fingers, the fingers of saidlaminations of said core structure aligned to define a plurality ofslots extending transversely of the laminations, a plurality ofcircumferentially equispaced liners mounted in said slots, said linersbeing of substantially the same configuration and weight and all of saidliners being substan tially equispaced from the axis of rotation of saidrotor, at least one of said liners being a thin laminated linerconsisting of a thin layer of electrically conductive material havingone face in contact with a plurality of said laminations and a thinsheet of insulating material confronting the face of said layer oppositesaid one face, said one liner being generally of U-shaped cross sectionwith the open side aligned with the slot and having at each opposite endthereof a turned-back flange portion adapted to overlie the end face ofthe laminations at each end of the core structure thereby to provide agood electrical connection at opposite ends of the core structure, andan armature winding in said slots pressing said one liner intoengagement with said lamination thereby to decrease the electricalresistivity of said core structure, said one liner being readilydeformable under the pressure of the windings and said windings beingtightly wound whereby the direct contact between the layer ofelectrically conductive material of said one liner and said laminationsconstitutes the sole electrical connection therebetween.

References Cited by the Examiner UNITED STATES PATENTS 493,025 3 l 893Hassler 310-265 1,316,798 9/1919 Lamme 310-183 1,974,406 9/1934 Apple310-217 2,483,066 9/1949 Sigmund et al 310-215 3,130,335 7/1964 Rejda310-215 MILTON O. HIRSHFIELD, Primary Examiner.

M. L. LEVY, L. L. SMITH, Assistant Examiners.

1. A BALANCED ROTOR ASSEMBLY FOR AN ARMATURE COMPRISING A CORE STRUCTUREINCLUDING A PLURALITY OF LAMINATIONS EACH HAVING A PLURALITY OF SPACEDAPART FINGERS, SAID LAMINATIONS ARRANGED IN FACE-TO-FACE RELATION WITHTHE FINGERS ALIGNED TO DEFINE A PLURALITY OF SLOTS EXTENDINGTRANSVERSELY OF THE LAMINATIONS, A PLURALITY OF CIRCUMFERENTIALLYEQUISPACED LINERS MOUNTED IN SAID SLOTS, SAID LINERS BEING OFSUBSTANTIALLY THE SAME CONFIGURATION AND WEIGHT AND ALL OF SAID LINERSBEING SUBSTANTIALLY EQUISPACED FROM THE AXIS OF ROTATION OF SAID ROTOR,AT LEAST ONE OF SAID LINERS BEING A THIN LAMINATED LINER CONSISTING OF ATHIN LAYER OF ELECTRICALLY CONDUCTIVE MATERIAL HAVING ONE FACE INCONTACT WITH A PLURALITY OF SAID LAMINATIONS AND A THIN SHEET OFINSULATING MATERIAL CONFRONTING AND BONDED TO THE FACE OF SAID LAYEROPPOSITE SAID ONE FACE AND AN ARMATURE WINDING IN SAID SLOTS PRESSINGSAID ONE LINER INTO ENGAGEMENT WITH SAID LAMINATIONS THEREBY TO DECREASETHE ELECTRICAL RESISTIVITY OF SAID CORE STRUCTURE, SAID ONE LINER HAVINGAN OPEN SIDE ALIGNED WITH THE SLOT AND BEING READILY DEFORMABLE UNDERTHE PRESSURE OF THE WINDINGS AND SAID WINDINGS BEING TIGHTLY WOUNDWHEREBY THE DIRECT CONTACT BETWEEN THE LAYER OF ELECTRICALLY CONDUCTIVEMATERIAL OF SAID ONE LINER AND SAID LAMINATIONS CONSTITUTES THE SOLEELECTRICAL CONNECTION THEREBETWEEN AND SAID WINDING BEING EXPOSEDTHROUGH SAID SLOTS.